The upgrading of heavy charges, commonly called residues, (straight-run residue, vacuum residue, deasphalted oils, etc.), by catalytic cracking requires modifications of the refining system in the oil industry.
For example, a pretreatment, in particular removing to a maximum extent coke and metals, which poison the catalyst, is considered hereinafter.
When the charge to be treated has maximum Conradson carbon (CCR) and metal contents of respectively 6-8% and 20-30 ppm (parts per million), the use of processes of the cracking type with fluid bed in an elongate tubular enclosure seems appropriate. On the contrary, when the charge is heavier (CCR&gt;10) and mainly when its nickel and vanadium content reaches several hundred of ppm, the pretreatment is necessary, in view the performances of the catalysts presently available on the market. Several pretreatment techniques already exist, particularly delayed coking, fluid coking, hydrotreatment, deasphalting etc...
U.S. Pat. No. 4,243,514 discloses a pretreatment of the charge, in an enclosure provided therefor, by vaporizing the charge in admixture with previously heated inert solid particles. These particles have often sizes ranging from 20 to 150 .mu.m and are directly generated in the regenerator by atomization of clay muds for example. The obtained microspheres are characterized by their low specific surface limiting the conversion rate to a low level. Nevertheless, they provide for the collection of 95% of the metals and of substantially the total amount of the asphaltenes initially contained in the charge. But the released effluents, forming a satisfactory charge for catalytic cracking in fluidized bed (F.C.C.), must be cooled before being conveyed to a catalytic cracking zone separate and distant from that where the pretreatment is performed, in order to reduce to a minimum the risk of thermal cracking, which would otherwise occur in view of the length of the passageway and in view of a substantial residence time at high temperature with, as a result, coke formation being favored in the conversion.